The invention is directed to a sieve filter for fluid conduits according to the features of the preamble of claim 1, and it is especially advantageously suited for hydraulic pressure lines in internal combustion engines.
It is generally known to the person skilled in the art that, after assembly of the individual parts of an internal combustion engine, it cannot be avoided that some finishing-related dirt particles, such as shavings, jointing solution residues and the like, remain in the interior of internal combustion engines despite cleaning of the individual parts. Especially with internal combustion engines which are outfitted with a hydraulic device for relative rotation of the camshaft in relation to the crankshaft of the internal combustion engine, there exists the danger that these dirt particles enter into the lubricant circulation of the internal combustion engine from which mostly the device for relative rotation of the camshaft is also hydraulically supplied. Since as a rule an electromagnetic control valve is connected in series ahead of this device, which controls the fluid feed and removal to and from this device through one of the camshaft bearings in the cylinder head of the internal combustion engine, it is consequently not to be ruled out that if dirt particles exceed a certain magnitude, they will cause impairments in the function of the control valve up to possibly completely blocking it. A thorough cleaning of the individual parts of the internal combustion motor for avoiding these impairments of function has, however, above all in mass production, proven to be uneconomical, so that in order to create a remedy, first of all a fine mesh wire filter was incorporated into the oil channel to the electromagnetic control valve of the device. This filter indeed protects the control valve from the penetration of dirt particles, but in practice it has nonetheless become apparent that if the filter becomes completely stopped up, not only do malfunctions occur with the device to be controlled, but also to an undersupply of lubricants to the camshaft bearings which, in the worst case, may result in total failure of the internal combustion engine due to bearing seizures.
Another sieve filter is known, which was actually provided for incorporation into the flow pathway of a hydraulic signaling device of a fuel injection pump for an internal combustion engine, but also appears suited to solve the aforementioned problem due to providing a bypass function for the case of paraffin stoppage of its filter element at extremely low temperatures. This is disclosed in the genus-forming DE 37 18 068 C1. This rod-like sieve filter basically consists of an annular disk-like fluid inlet and a likewise annular disk-like fluid outlet, between which the filter element subject to fluid flow and supported by stiffening bars is arranged. The filter element is constructed as tapering in the direction of flow and is in each case connected with the fluid inlet fit into the pressure conduit as well as with the fluid outlet having a smaller diameter through the ends of its stiffening bars. In the interior of the sieve filter, there in addition extends over the entire length of the filter element a bypass pipe arranged concentrically in relation thereto, the inlet side of which is situated in the area of the fluid inlet and the outlet side of which is sealingly connected with the fluid outlet. On the inlet side, the bypass pipe has a pressure relief valve which can open against a spring force. The relief valve has a ball as a closing member, and the valve seat is situated at the entrance of the bypass pipe.
The disadvantage with these known sieve filters is, however, that their manufacture, due to the bypass pipe with the pressure relief valve, demands a relatively high manufacturing expenditure and costs. Equally, the relatively large space requirement for such a sieve filter has proven disadvantageous since this only guarantees an optimal function when constructed appropriately long and narrow.
For this reason, underlying the invention is the object of providing a sieve filter for fluid conduits, especially for hydraulic pressure lines in internal combustion engines which is constructed compactly and space-saving and whose manufacturing expenditure and cost are reduced to a minimum.
In accordance with the invention, this objective is accomplished with a sieve filter according to the preamble of claim 1 such that the fluid inlet of the sieve filter itself is constructed with the bypass function in that first, the inlet has a smaller external diameter than the fluid outlet of the sieve filter, that is constructed with the same diameter of the pressure line, and in that secondly, this is sealed off by a pressure relief valve arranged in the interior of the sieve filter. Here the fluid inlet is coaxially fixed in position in the pressure conduit by distancing elements arranged on its outer diameter, between the interstices of which the fluid is passed when the filter element is not clogged or is filtered by the filter element when viscosity is normal along the internal walling of the pressure line. When the filter element is clogged or when the fluid is highly viscous, the fluid inlet is in contrast, clearable through an opening of the pressure relief valve as a bypass entrance resulting from the rise of fluid pressure in front of the sieve filter, through which the fluid is passed along the interior of the filter element unfiltered to the fluid outlet.
In an appropriate refinement of the sieve filter constructed in accordance with the invention, the stiffening bars of the filter elements are fastened with their outlet side ends on the internal side ring surface of the fluid outlet, while the inlet side ends of the stiffening bars of the filter elements are constructed with axial extensions which are connected with the outer surface of the fluid inlet. The axial extensions of the inlet side ends of the stiffening bars here project above the fluid inlet and are at the same time constructed as its radial distancing elements toward the interior walls of the pressure line which are coaxially fixed into position with those of the fluid inlet in the pressure line. Here it is, however, also possible to construct the inlet side ends of the stiffening bars of the filter elements without axial extension and to fasten them on the interior side ring surface of the filter inlet as well as to arrange separate distancing elements toward the interior walling of the pressure conduit on the outer surface of the fluid inlet with which the fluid inlet is fixed in position in the pressure conduit.
A further feature of the sieve filter constructed in accordance with the invention is that the pressure relief valve in the interior of the sieve filter preferably is formed by a valve ball lying on the fluid inlet as well as a prestressed spring element supported at the fluid outlet and on the valve ball. The spring element is preferably constructed as a compression coil spring, while the valve ball is a steel ball which together with the compression coil spring is inserted through the opening of the fluid inlet of the sieve filter into the sieve filter. Into this opening of the fluid inlet, an additional complementary annular disk is insertable which preferably is locked by means of a clip connection in the fluid inlet and which has on the filter interior side a concave recess constructed as an inlet-side back pressure surface for the valve ball of the pressure relief valve. It is also conceivable, however, to manufacture the fluid inlet and the annular disk insertable into this in one piece and to fasten this part after insertion of the valve ball and the compression coil spring in the sieve filter through a clip connection on the stiffening bars of the sieve filter. It is equally possible to insert, instead of the valve ball, a valve ball with a corresponding valve seat in the additional annular disk or also a cylindrical valve plate without valve seat in the annular disk into the sieve filter.
Furthermore, it is additionally proposed in configuring the sieve filter constructed according to the invention that the stiffening bars of the sieve filter carry the filter element of the sieve filter between its inside and outside which extends coaxially from the fluid inlet to the fluid outlet. For optimal support of the filter element, four evenly peripherally distributed stiffening bars have proven most advantageous here in which in the preferred manufacture of the sieve filter by plastic injection molding, the filter element is cast in. The exterior sides of the stiffening bars at the same time have in the area of axial extension of the filter element a distance toward the interior walling of the pressure line in order to be able to guarantee, by an uninterrupted annular space around the filter element, an evenly distributed fluid flow through the filter element as well as a greater fluid throughput through the filter element. At the same time the interior sides of the stiffening bars are constructed in the same area as guide paths for the valve ball of the pressure relief valve, whereby, for attaining the greatest possible guide surface on the stiffening bars, a construction of the stiffening bars with a rectangular or square contour cross section as well as with concavely constructed interiors has proven especially advantageous.
Finally, it is furthermore proposed in preferred application of the sieve filter constructed in accordance with the invention that the hydraulic pressure conduit or line into which the sieve filter is inserted is preferably constructed as an oil channel to a device for relative rotation of a camshaft in relation to a crankshaft of an internal combustion motor. This hydraulic device is supplied with hydraulic fluid in a known manner from the lubricant circulation of the internal combustion engine, whereby an electromagnetic control valve is connected in series before the device which controls fluid delivery and removal to and from the device through one of the camshaft bearings in the cylinder head of the internal combustion engine.
The oil chamber connected with the lubricant pump and leading to this device for this reason opens first axially or radially into a continuing bore hole with a larger diameter which is provided to accommodate the cylinder valve element of the electromagnetic control valve for the device, and is worked into the cylinder head of the internal combustion engine or into a valve housing fastened on the cylinder head of the internal combustion engine. The base hole here preferably has such a depth that the sieve filter together with the valve element of the electromagnetic control valve is inserted into the base hole and can be axially fixed in position directly in front of the valve element. The axial fixing into position of the sieve filter here takes place such that, on the one hand the inlet side extensions of the stiffening bars of the filter elements lie on the bottom of the base hole, and on the other hand is supported with the fluid outlet on the face of the valve element of the electromagnetic control valve. The arrangement of the sieve filter in the base hole of the valve element of the electromagnetic control valve consequently enables a compact and space saving construction of the sieve filter whereby the sieve filter nonetheless can also be arranged, through local diameter extensions, inside the oil duct or through a narrower design at any place before the electromagnetic control valve of the device.
The sieve filter constructed in accordance with the invention, especially for hydraulic pressure lines in internal combustion engines, consequently has in comparison with the sieve filters known on the basis of the state of the art, the advantage that its bypass function is integrable without additional components such as bypass pipes or the like into the existing components so that the sieve filter can be constructed as compact and space-saving overall and can be manufactured with the lowest finishing and expenditure possible.